Disposable endoscope

ABSTRACT

An endoscope includes a disposable probe and a non-disposable focusing ocular. The probe includes a transfer module assembly including one or more relay modules, and an objective element including a distal glass window, a molded plastic prism and three molded plastic lenses. Each of the relay modules contains an entry glass rod, an intermediate glass rod, and an exit rod, each having flat end surfaces and two identical molded plastic doublets. The elements of the ocular are all of glass and include an axially movable focusing doublet and two non-movable doublets. The disposable probe introduces certain aberrations into the image. The non-disposable focusing ocular corrects these aberrations. A single curved surface is formed on the distal glass window of the probe; all other curved optical surfaces of the disposable probe are formed on molded plastic members, thereby reducing the cost of the probe sufficiently to be cost-effective for single patient, disposable use.

This is a divisional application of application Ser. No. 08/223,409filed Apr. 4, 1994, now U.S. Pat. No. 5,519,332 which is a continuationof application Ser. No. 07/833,406, filed Feb. 6, 1992 now U.S. Pat. No.D 336,512.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to endoscopes and, more particularly, toendoscopes manufacturable sufficiently inexpensively to be disposableafter single patient use, while being at least equal in opticalperformance to conventional endoscopes requiring sterilization.

2. Description of the Prior Art

Endoscopic or least invasive surgery has many advantages overconventional "open" surgery. Patients who have undergone endoscopicsurgery rather than open surgery experience vastly less trauma and muchfaster recoveries, leading to improvement in the quality of health caretogether with reduction in the cost of health care. These advantageshave spurred extensive development of endoscopes.

The term "endoscope" as used herein refers to an elongated optical probecapable of presenting a visible image of the interior of a body cavity,joint, organ or the like to a physician on either an eyepiece or a videoscreen. The endoscope is typically introduced into the body cavitythrough a bore in another device (also typically referred to in the artas an endoscope, or as an endoscope sheath) including a light source aswell as other bores for introducing surgical instruments, water, air,suction and the like. Endoscopes as optimized for various surgicalprocedures are referred to as arthroscopes, cystoscopes, proctoscopes,laparoscopes and the like.

The art has for some years sought to develop a suitable disposableendoscope. The surgical requirement of absolute sterility is difficultto satisfy with conventional endoscopes as these complex instruments arenot readily amenable to conventional sterilization techniques. Thespread of infectious disease is of particular concern and requires thatcare and caution be employed during the sterilization process.Accordingly, there is a strong need for a suitable disposable endoscope,that is, one made sufficiently inexpensively as to be cost-effective fordisposal after single-patient use.

Endoscopes typically consist of a distal objective for forming anoptical image of the interior of the body cavity, bone, joint or organ,a transfer module (sometimes termed a "relay section") for transmittingthe image from the distal end of the probe to its proximal end, and anocular at the proximal end of the transfer module for presenting theimage to an eyepiece, a video camera or the like. Typically, the ocularwill contain the movable focusing components of the endoscope.

One of the difficult tasks in designing a satisfactory endoscope is thatof designing the transfer module. The transfer module must be capable oftransmitting the image formed by the objective to the ocular withoutsignificant loss of brightness or sharpness in the image. Early designsincluded numerous glass refractive elements, each requiring extensivepolishing. The high cost of manufacture precluded use of these designsfor disposable endoscopes.

More recently it has been suggested that the refractive optical elementsof the transfer module should be molded of plastic, while thetransmitting elements could be formed of much less expensive plano glassrods, i.e. glass rods having flat ends. Indeed, provision of the curvedsurfaces in optical systems by employment of molded plastic members, andusing glass only for flat surfaced elements, is suggested by opticaldesign textbooks; see, e.g., The Handbook of Plastic Optics, 2ndedition, published by U.S. Precision Lens, Inc. (1983), at page 86.However, despite this suggestion, there is no prior art disclosure orteaching of an endoscope providing adequate optical performance capableof manufacture at sufficiently low cost to be disposable.

Prior art endoscopes have typically been designed such that theobjective provides a self-corrected image to the transfer module, theimage then being transmitted with as little further aberration aspossible to an ocular group. It is also known to employ the transfermodule to correct aberration introduced by the objective. In either casethe image presented by the probe to the objective is fully corrected.Typically the ocular designs employed have included two doublets placedback to back; this form permits separating the doublets at an afocalspace. The first doublet is employed as a simple magnifier of the image,and the second doublet as a focusing element to allow a video camera toform the visible image on a display screen. However, this essentiallysimplified ocular design requires the image formed by the combination ofthe objective and the transfer module to be self-corrected. The cost ofmanufacture of suitable objective and transfer module components is toogreat for single patient disposable use.

Prior endoscopes have commonly also employed a fore-oblique prism in thetip of the endoscope to provide an off-axis field of view, that is,centered about an axis at an angle to the optical axis of the probe, sothat by rotating the probe the surgeon has an effectively wider field ofview than otherwise possible. In the prior art, such fore-oblique prismshave been manufactured by separately manufacturing two or three prismsof glass of high refractive index, separately coating the appropriatesurfaces with reflective material, bonding the prisms together in anassembly jig requiring very high precision, and finally grinding theouter surface of the assembly to the desired cylindrical form, Thesemanufacturing steps are very labor intensive and time-consuming, andrender such fore-oblique prisms in the prior art much too expensive foruse in a disposable device for single patient usage.

Another constraint on endoscope design arises because from time to timeduring surgery the surgeon may wish to change the endoscope's viewingangle, that is, to vary the angle between the center of the field ofview and the optical axis of the probe. While endoscope designs havebeen proposed permitting variation of the viewing angle by moving apivoted mirror or the like at the distal tip of the endoscope, thesedesigns have been highly impractical. Variation of the viewing angle ispossible in practical endoscopes only by removing a first probe from thesurgical portal and substituting a second probe having a differentviewing angle. To do so employing conventional re-usable endoscopesrequires sterilization of several different endoscopes at substantialcost. If a video camera were being used to display the image, as istypical, this procedure would normally also necessitate disconnectingthe ocular of the first endoscope from the video camera and reconnectinga second endoscope. It would be desirable to provide disposableendoscope probes having differing viewing angles all mating with thesame nondisposable ocular, so that the probe could be replacedconveniently and discarded at reasonable cost if the surgeon desired tochange viewing angles.

Endoscopic objectives found in the prior art have required glasselements of very high refractive index and having large differences intheir spectral dispersion to provide control of optical aberration.These prior art designs have been limited to all-spherical surfacedesign forms because of the cost of producing aspheric surfaces inglass. More specifically, one prior art endoscope objective design formuses a plano-concave flint glass element of very high refractive indexpreceding the prism element, a high index of refraction convex crownglass element bonded to the preceding prism element, a high index ofrefraction biconvex crown glass element, and a doublet including oneelement each of crown and flint glass. In the prior art, the high costof production of these elements, having optical surfaces sufficientlysteep to require individual polishing, had precluded use of this designfor a disposable endoscope.

Until the present invention, there has been provided no design for anendoscope including a disposable probe that provides satisfactoryoptical performance, including convenient variation of viewing angle,while being manufacturable sufficiently inexpensively to becost-effective for single-patient disposable use.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above-mentioneddisadvantages of prior art disposable endoscopes.

More particularly, it is an object of the invention to provide anendoscope capable of providing a satisfactory visual or video image to asurgeon of the interior of a body cavity, bone, joint, vessel or organ,and including a probe manufacturable sufficiently inexpensively to becost-effective for disposability after single-patient use.

It is a particular object of the invention to provide an objectivedesign for an endoscope having its principal optical elements molded ofplastic, and to thus greatly lower the cost of the endoscope as comparedto prior art designs.

It is a further object of the invention to provide a disposableendoscope probe and, in particular, a disposable endoscope probecomprising a prism for providing oblique viewing angles requiring nocomplex and time-consuming assembly operations.

It is an object of the present invention to provide a transfer modulefor an endoscope that does not employ long glass rods but employs onlyshort glass rods, rendering the device much less susceptible tobreakage.

It is an object of the invention to provide an endoscope featuringessentially interchangeable disposable probes used with the same ocularand, in particular, to provide a selection of disposable probes havingvarious viewing angles between the center of the field of view and theaxis of the probe.

It is another object of the invention to provide a number of probes foran endoscope, each probe providing a different viewing angle, the probesdiffering only in the design of the prism but using essentially commoncomponents elsewhere, thus substantially economizing probe manufacture.

It is a further object of the invention to provide an endoscopecomprising a disposable probe, including an objective group and atransfer module assembly, and a non-disposable ocular.

It is a further objective of the invention to provide an endoscopecomprising a disposable probe and a non-disposable focusing ocular,wherein certain residual aberration is present in the image formed bythe disposable probe and transferred to the ocular, and wherein thenon-disposable ocular corrects the residual aberration in the imageformed by the probe.

The above objects of the invention and needs of the art are satisfied bythe present invention of an endoscope comprising a disposable probe anda non-disposable focusing ocular. The disposable probe is sufficientlyinexpensive to be cost-effective for disposability after single patientuse. The endoscope of the invention suffers no performance disadvantagecompared to conventional non-disposable endoscopes.

The disposable probe of the present invention comprises an objectivegroup at its distal end and a transfer module assembly. The objectivegroup comprises a single glass window element at its distal end, amolded plastic prism and three molded plastic elements. The transfermodule assembly comprises a number of identical relay modules. In thepreferred embodiment, each relay module comprises two doublets withinterspersed plano-surfaced glass rods. The doublets each include twomolded plastic elements. The disposable probe introduces certainresidual aberrations into the image presented to the non-disposablefocusing ocular of the endoscope. The focusing ocular corrects for theseaberrations, and optically couples the disposable probe to a videocamera or the like.

The focusing ocular comprises a first movable focusing doublet and fourfurther lens elements, all of glass. Relatively steep spherical surfacesare formed in these lens elements to correct chromatic aberration, fieldcurvature, and astigmatism in the image presented by the transfermodule. However, no aspheric surfaces are required in the non-disposablefocusing ocular.

A generally cylindrical molded plastic prism in the objective is used toprovide a field of view angled with respect to the optical axis of theprobe. The prism is a unitary solid element. An inclined distal end ofthe prism is directly juxtaposed to the rear surface of a planar glasswindow element at the distal end of the probe. Light entering the glasswindow normal to its surface enters the prism through a first angledend, reflects internally at two reflecting surfaces formed by recessesin the prism, and exits the prism directly along the optical axis of theprobe. The refractive index of the plastic of the prism and the angle atwhich the light rays meet the plastic/air interface of at least one ofthe reflecting surfaces are such that reflection occurs by totalinternal reflection within the prism. Accordingly, no more than a singlereflecting surface of the prism requires a reflective coating, providinga further economy. The components of the objective, apart from theprism, are identical in several embodiments of the probe havingdiffering viewing angles.

The overall design of the endoscope of the invention thus provides theadvantage that the only glass elements employed in the disposable probeare the window element at the distal end of the probe, a plano surfacedwindow at the proximal end of the transfer module, and the planosurfaced glass rods of the transfer module. These elements are allrelatively economical to manufacture. The objective contains the windowelement, one prism, and three lenses (two of which are identical) whilethe transfer module only includes two types of lens elements. Each ofthe lenses in the probe is molded of plastic and accordingly isrelatively inexpensive in quantity. The lenses of the disposable probeand the prism may be molded of glass instead of plastic; thesealternatives are anticipated to become increasingly attractive as glassmolding technology matures.

The non-disposable focusing ocular contains six glass lenses, eachincluding only spherical surfaces. The use of glass elements in thefocusing ocular lends durability, and the cost of these glass elementsis not significant to the overall cost effectiveness of the endoscope ofthe invention.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodimenttaken in conjunction with the accompanying drawings wherein like partsin each of the several figures are identified by the same referencecharacters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded side view of an endoscopic imaging systemaccording to the present invention;

FIG. 2 is a side view of the optical components of the disposable probeand non-disposable ocular of the endoscope of the present invention;

FIG. 3 is a view in longitudinal section of the objective assembly ofthe disposable probe of the endoscope of the present invention;

FIG. 4 is a side view of one of the transfer modules of the transfermodule assembly of the probe of the endoscope of the present invention;

FIG. 5 is an optical schematic diagram of the optical components of thenon-disposable focusing ocular of the endoscope of the presentinvention;

FIG. 6 is a proximal end view of the prism of the disposable probe ofthe endoscope of the present invention;

FIG. 7 is a view in plan of the prism from its underside;

FIG. 8 is a distal end view of the prism;

FIG. 9 is a top view in plan of the prism;

FIG. 10 is a view in section of the prism taken along the line 10--10 ofFIG. 6;

FIG. 11 is a view in section of a mold suitable for manufacture of theprism;

FIG. 12 is a plot of surface sagitta versus radius specifying theterminology employed to define the aspheric surfaces of lenses in theprobe of the endoscope of the present invention;

FIG. 13 is a ray-tracing diagram showing the paths of various light raysthrough the endoscope of the invention, illustrating the positions ofintermediate images formed therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded view of the principal components of a completeendoscope assembly according to the invention. The disposable probe 10of the endoscope includes an elongated probe section 12 and atermination 14. The termination 14 comprises a male member 16 receivedin a recess formed in the body of a non-disposable focusing ocular 20 ofthe endoscope. The male member 16 may be releasably coupled to the bodyof the ocular 20 in generally conventional fashion. The art is aware ofsuitable focusing mechanisms for the ocular 20. The ocular 20 in turn ismated with a video camera 22 or other image forming device in agenerally conventional manner well understood by those of skill in theart. As discussed in detail below, the endoscope of the presentinvention is preferably used in conjunction with a video camera 22including a so-called "CCD" imaging element and spectral and spatialfilter elements.

FIG. 2 is a side view of the complete optical system of the endoscopeaccording to the invention. The external shapes of the termination 14and ocular 20 are shown in phantom to clarify the relation of thesesections of the complete endoscope, but this is not a limitation on theprobe of the present invention. The disposable probe 10 comprises anobjective group 24 and a transfer module assembly 26. Transfer moduleassembly 26 comprises three essentially identical relay modules 28, 30and 32. The relay modules can be multiplied as needed to obtain thedesired total probe length; preferably, an odd number of the relaymodules is employed to insure that the image is not inverted at theproximal end of probe 10.

As can be seen in FIG. 2, the objective comprises an end window element34, a prism 36, and three lenses 38, 40 and 42. The structure of theobjective 24 is discussed in detail below in connection with FIG. 3.Only the end window element 34 is glass; the prism 36 and the lenses 38,40 and 42 are all molded of plastic, greatly reducing the overall costof the disposable probe 10.

In the example of the endoscope of the invention shown in FIG. 2 anddiscussed throughout this specification, the three relay modules 28, 30and 32 making up the transfer module assembly 26 together comprise sevenplano ended glass rods 44, 45, 46, 47, 48, 49 and 50. Six doublets, eachcomprising molded plastic lenses 52 and 53, are disposed between eachpair of glass rods 44-50. The respective positions of lenses 52 and 53are reversed where they appear in alternating positions along thetransfer module assembly. The transfer module assembly 26 is terminatedby an optical window 56 disposed at its proximal end, and is describedin detail below in connection with FIG. 4.

The focusing ocular 20 comprises a window 58 designed to be disposed inclose proximity to but not touching window 56. Ocular 20 comprises afirst glass doublet, comprising elements 59 and 60, which is axiallymovable to focus the image, a second doublet comprising glass elements62 and 64, and a third doublet including elements 66 and 68. Thefocusing ocular 20 is described in detail below in connection with FIG.5.

Having now briefly identified the components of the disposable endoscopeof the invention, a discussion will now be provided of the structure andfunctions of each. Subsequently the detailed optical specifications ofeach of the elements will be presented.

As discussed above, the endoscope of the present invention comprises adisposable probe 10, the probe 10 including a distal objective 24 forforming an image and a transfer module assembly 26 for transferring theimage from the distal end of the probe to the proximal end of the probe,and a focusing ocular group 20 for presenting this image to a videocamera 22 or equivalent device for providing a visible image. The priorart has invariably (so far as known to the present inventor) attemptedto provide self-correcting endoscope probes; that is, the prior art hasattempted to provide endoscope probes forming an image including noresidual aberration to be corrected by the focusing ocular. The priorart suggests that one element of an endoscope probe may be designed tocorrect optically for aberration introduced by another group of theprobe. For example, in Yamashita et al U.S. Pat. No. 4,165,917 theastigmatism of the objective is corrected by the relay lens group (i.e.the transfer module), whereby the image presented to the ocular is fullycorrected. However, as mentioned above, the art does not suggest thataberrations introduced by the probe might usefully be corrected by theocular.

According to an important feature of the present invention, the imageprovided by the probe is permitted to include certain aberration to becorrected by the focusing ocular. The aberration in the image providedby the probe is sufficiently severe that if the image were not correctedit would be considered unacceptably distorted. Correction by the ocularof residual aberration in the image formed by the probe permits verysubstantial simplification of the optical design of the disposable probeof the invention, reducing the cost of the probe such that it iscost-effective for disposability after single patient use. Inparticular, this has enabled placement of substantially all costly glasselements having curved surfaces in the non-disposable ocular 20, whilethe disposable probe 10 principally includes molded plastic focusinglenses and plano-ended glass rods.

More specifically, relatively large amounts of field curvature, axialchromatic aberration, and lateral chromatic aberration, as well asastigmatism, exist in the image formed by the disposable probe 10 of theinvention, but the image is nearly completely corrected with respect tospherical aberration and coma. The non-disposable ocular 20 comprisesoptical glass elements eliminating the residual aberration in the imageprovided by the disposable probe. Of course the ocular 20 must alsocorrect any optical aberration introduced by its own design. The ocular20 also includes an axially movable glass doublet for focusing theendoscope of the invention. Provision of the focusing mechanism in thenon-disposable ocular rather than in the disposable probe furtherreduces the cost of the probe.

Referring now to the individual elements of the probe of the invention,the individual surfaces through which rays from the object pass areidentified herein and in the accompanying drawings and claims, and arespecified in Table I below, by individual surfaces numbered S₁ to S₇₁,reading from the distal tip of the probe to the imaging surface of a CCDsensor comprised by the video camera 22.

The objective 24 comprises a glass window element 34 at the distal tipof the probe, the prism 36, and three optical elements 38, 40, and 42.The glass window element 34 at the tip of the probe providessatisfactory bio-environmental compatibility. Window element 34 has aplanar distal surface S₁ and a concave lens surface S₂ (see FIG. 3)formed on its inner planar surface for broadening the field of view ofthe probe. The plano-concave window element 34 is formed of a high indexof refraction crown glass providing improved control of the lateralchromatic aberration of the objective. Lateral chromatic aberrationintroduced by the window 34 is corrected by the use of a high indexflint-like optical plastic for the prism 36, which also corrects lateralchromatic aberration introduced by the two elements 38 and 40immediately following the prism.

An equivalent front window element 34 might be manufactured convenientlywith an aspheric inner surface. This can be accomplished by fabricatinga glass substrate having a planar outer surface and a spherical concaveinner surface. A quantity of suitable optical plastic or resin materialis disposed in the concavity, and pressed against an aspheric moldmember under suitable conditions of temperature and pressure to mold theaspheric surface. Such processes are generally known to the art.

The prism 36 of the present invention is a unitary injection moldedmember made of a moderately high refractive index material such as NAS(an acrylic/polystyrene copolymer). As noted above, as glass moldingtechnology matures, it may become feasible to mold the prism of glass.The prism has two internal reflecting surfaces S₄ and S₅ so that theimage retains its proper image "hand". In the embodiment shown of prism36, whereby the field of view is inclined at 25° to the optical axis ofthe probe 10, the refractive index of the material of the prism 36 andthe angles of the reflecting surfaces S₄ and S₅ can be chosen such thatreflection takes place at surface S₅ according to total internalreflection. Accordingly, only reflecting surface S₄ need be coated witha layer 73 of reflective material, further simplifying and reducing thecost of the manufacturing operation.

The prism 36 is generally cylindrical, having a distal planar surface S₃juxtaposed to glass window element 34 at the tip of the probe 10.Surface S₃ and window element 34 are inclined at an angle to the opticalaxis of the prism normal to the center of the field of view of theprobe. The proximal planar surface S₆ of the prism 36 is orthogonal tothe optical axis of the probe. In this way, both the entry and exitsurfaces of the prism 36 are perpendicular to rays along the opticalaxis, for control of optical aberration.

Three molded plastic lenses 38, 40, and 42 follow the prism in theobjective group 24. Lenses 38 and 40 are physically identical, but theirrelative orientations are reversed. The third lens 42 is unique. The twoidentical lens elements 38 and 40 each include one aspheric surface(these being identified as surfaces S₈ and S₉ in FIG. 3) and onespherical surface (S₇ and S₁₀). This arrangement provides improvedcontrol of spherical aberration and astigmatism. Aberration control bythe aspheric surfaces S₈ and S₉ is necessary due to the effectivelocation of the aperture stop in the center of the fore-oblique prism36; some rays pass through the two central elements far from the opticalaxis.

The final element of the objective, lens 42, is also injection molded,from a flint-like optical plastic material. Use of the flint-likematerial permits this element to compensate for much of the axial andlateral chromatic aberration introduced by the preceding elements. Thechoice of an uncemented final element 42 permits its front surface S₁₁to be curved independently of element 40, compensating for astigmatismintroduced by the preceding elements.

The elements of the objective are spaced from one another by air gaps.Precise control of the lengths of the air gaps is provided by spacermembers 76, 77, 78, 79 and 80 integrally molded around the peripheriesof the optical surfaces. These integral spacers eliminate the need forseparate small components, avoiding the cost of their fabrication andassembly. A further spacer 82 is provided between the third element 42of the objective and the first glass rod 44 of the transfer moduleassembly 26. The inner periphery of spacer 82 is the field stop,identified as surface S₁₃. The field stop 82 is thus physically locatedbetween the proximal element 42 of the objective and the transfer moduleassembly 26.

As described above, in a typical endoscope according to the presentinvention the transfer module assembly 26 may be considered to comprisethree substantially identical relay modules 28, 30 and 32. The transfermodule assembly is shown in further detail in FIG. 4. The number ofrelay modules in the transfer module assembly can be extended more orless indefinitely, although odd numbers of relay modules are typicallyused to preserve image orientation.

The relay modules 28, 30 and 32 each comprise an entry glass rod, afirst doublet, an intermediate glass rod, a second doublet, and an exitrod. The exit rod of one relay module and the entry rod of thesucceeding rod are preferably configured as a single rod, as shown. Asdiscussed in detail below in connection with FIG. 13, intermediateimages are formed within the glass rods extending between the relaymodules. By thus forming the intermediate images within the rods, ratherthan at their surfaces or in air gaps between the rods, the possibilityis eliminated that a scratch or other defect on a rod end surface mightinterfere with formation of a suitable visible image.

The transfer module assembly 26 may also usefully be considered tocomprise a number of relay subgroups 33, each comprising a doublet andan intermediate rod, juxtaposed to one another to make up the bulk ofthe length of the transfer module assembly. As thus defined, two relaysubgroups 33 make up a relay module; the complete transfer moduleassembly shown in FIG. 4 is made up of five identical subgroups 33, arelatively short glass entry rod 44, and an exit subgroup including asixth identical doublet and a relatively short exit glass rod 50.

Each of the glass rods 44, 45, 46, 47, 48, 49, and 50 of the transfermodule assembly is plano-ended, reducing cost. Further, rods 45-49 areof identical length, again reducing cost. The surfaces of rods 44-50 areidentified in FIG. 4 corresponding to the listings of the rods in TableI below. Thus, the entry surface of the first glass rod 44 of the relaymodule 28 is identified as S₁₄.

The relay modules 28, 30 and 32 each further comprise two doublets eachincluding two molded plastic lenses 52 and 53. Lenses 52 and 53 are thusused twice in each relay module, with their orientation with respect toone another in each doublet being reversed according to the respectiveposition of the doublet within the relay module, as shown in FIG. 4. Asin the case of elements 38, 40 and 42 of the objective (FIG. 3), themolded plastic lenses 52 and 53 of each doublet preferably includeintegrally molded spacers (not shown) defining the air gaps betweenlenses 52 and 53 and the adjoining glass rods, to further simplifyassembly of the probe and reduce its cost.

One surface of element 53 of each of the doublets is aspheric, e.g.,surface S₁₉ of the first occurring element 53 and surface S₂₂ of thesecond occurring element 53. Aspheric surfaces are used in each element53 to substantially reduce the spherical aberration. Residual fieldcurvature and axial and lateral chromatic aberration are eliminated bythe optics of the ocular, as discussed previously.

Ideally, the two elements 52 and 53 of each of the doublets are cementedtogether to minimize alignment sensitivity and light loss. However, thisis not necessarily required; use of air-spaced doublets will furtherreduce the instrument cost.

An alternative to the use of an aspheric surface on one of the twoelements 52 and 53 of the doublets of the transfer module assembly is toreplace each of the doublets with a three-element system in whichaspheric surfaces can be avoided. As lenses having aspheric surfacescost no more to mold than spherical lenses, the embodiment shown ispreferred.

The principal advantage of the design shown is that the plano-endedglass rods can be manufactured very readily, since no curved glasssurfaces need to be polished. Employing only two types of molded plasticlens allows the lenses to be manufactured relatively inexpensively inhigh quantity by injection molding. As noted above, the lenses 52 and 53might equivalently be molded of glass rather than plastic.

As stated above, seven plano-ended glass rods 44, 45, 46, 47, 48, 49 and50 are used in the exemplary transfer module assembly shown in thedrawings. Rods 45, 46, 47, 48, and 49 are identical and their length iskept to a minimum to reduce the chance of breakage, a critical issue inarthroscopic and similar applications where physical stress on thedevice may be substantial. Rods 44 and 50 are of different lengths inorder to accommodate the objective and the ocular window geometries. Thechance of breakage is further reduced by provision of plastic spacers(not shown) integrally molded on the end of the intervening lenses 52and 53, since these spacers absorb much of the compressive stressencountered upon bending of the probe of an endoscope. Prior art designsemploying metal spacers between glass lenses force the compressivestresses to be absorbed by the fragile glass components. Alternativeembodiments of this invention reduce the rod lengths to further minimizethe chance of breakage by dividing rods 45, 46, 47, 48 and 49 into twoshorter identical rods with an intervening plastic spacer.

Referring now to FIG. 5, the ocular optical design comprises an axiallymovable cemented focusing doublet comprising elements 59 and 60 near anintermediate image location denoted by object surface S₅₆. Focusingdoublet 59, 60 bends the telecentric chief ray down toward the apertureof the following elements. Doublet 59, 60 also provides correction oflateral chromatic aberration. The ocular 20 also comprises a secondcemented doublet, comprising elements 62 and 64, and a third air-spaceddoublet comprising elements 66 and 68. The second cemented doubletcomprising elements 62 and 64 could also be designed as an air-spaceddoublet, but the cemented form is preferred since the manufacturingtolerances thereon are more forgiving. The second cemented doubletcomprising elements 62 and 64 provides most of the image forming powerof the system, and provides substantial correction of the axialchromatic aberration of the overall system.

The air-spaced doublet comprising elements 66 and 68 uses two glasstypes to permit correction of most of the lateral chromatic aberrationof the overall system. The airspace allows the juxtaposed surfaces S₆₅and S₆₆ of elements 66 and 68 to be strongly curved to correctastigmatism introduced by the remainder of the ocular group and tocorrect residual astigmatism and field curvature in the image receivedfrom the disposable probe 10.

As discussed above, the ocular 20 provides focus adjustment for changesin object distance by axial displacement of the focusing doublet 59, 60.Focus adjustment is effective for object distances from infinity to theouter surface of the objective window 34 with very little loss in imagequality. The use of weakly powered elements for focusing makes bothimage location and quality reasonably insensitive to radial displacementof the element during focus adjustment. Field curvature remaining in theimage received from the transfer module assembly 26 is corrected byconvex surface S₆₆ formed on element 68 of the ocular 20.

FIG. 5 also shows for completeness three plano-surfaced window elements70, 71 and 72 provided as part of the video camera 22 with which theendoscope of the invention is preferably utilized. Window 72 protectsthe CCD imaging element of the video camera 22. Window 71 is an infraredfilter, that is, a spectral filter removing infrared components from theimaged light. Substantially all CCD video cameras sold for endoscopicimaging purposes include suitable elements 71 and 72. The third windowelement shown is a spatial filter 70 provided in certain video camerassold for endoscopic imaging purposes by the Sony Corporation of Japan.Such spatial filters prevent aliasing of the image formed by the CCDelement, and their use is accordingly preferred. However, the endoscopeof the invention is useful with CCD video cameras not including suchspatial filters 70; accordingly, the detailed optical specificationsgiven below of the endoscope of the invention need not vary independence on the presence or absence of spatial filter 70.

FIGS. 6-10 provide details of the prism 36. Window element 34 is alsoshown in phantom in FIG. 10 for clarity. As can be seen, the prism 36 isa generally cylindrical solid member, having a first recess 90 formed inits "top" (in the orientation shown) and a second recess 92 formed inits "lower" surface. The innermost surface S₅ of recess 90 is planar, asis the innermost surface S₄ of recess 92. Rays entering the prism 36 ata distal inclined surface S₃ reflect in sequence from surfaces S₄ and S₅and exit the prism 36 through proximal planar end surface S₆. Line 100indicates the axis of the field of view. Lines 101 and 102 indicate thepath in the prism of the ray entering the prism along the axis of thefield of view 100. The ray exits the prism along line 103, that is,along the optical axis of the probe. The surface S₃ at which the prism36 is juxtaposed to the window 34 at the tip of the disposable probe ofthe endoscope according to the invention is normal to the axis of thefield of view of the endoscope defined by line 100. Rays from the centerof the field of view are thus normal to the oblique entry surface S₃ ofthe prism 36 and exit the prism orthogonal to the proximal exit surfaceS₆, in order to reduce aberration.

The detailed specifications of the prism vary with the desired viewingangle, that is, with the desired angle made between the axis 100 of thefield of view and the optical axis 103 of the probe. In the embodimentshown in FIGS. 6 through 10 this angle is 25°. Accordingly, angle A,between the distal surface S₃ and the optical axis, is 65°. Angle B, theangle between the first reflecting surface S₄ and the optical axis, is21.5°, and angle C, between the second reflecting surface S₅ and therear face of the prism 36, is 56°. Surface S₅ thus is oriented at anangle of 34° to the optical axis. It is within the scope of theinvention to provide prisms having different viewing angles which may,in some cases, exceed 90°, providing a retrograde field of view.Further, it is also within the scope of the invention to replace theprism 36 shown by a single cylindrical element in order to form an imageof a field of view directly centered on the optical axis of the probe.No modification to the optical design of the remainder of the objective,the transfer module assembly, or the ocular is required to do so.

It will be apparent by study of FIGS. 7 and 9 that if imaginarylongitudinal lines bisecting the reflecting surfaces S₄ and S₅ are drawnthey will intersect the optical axis, i.e., that the reflecting surfacesare longitudinally centered on the optical axis. Similarly, transverselines 104 and 106 drawn on each of the reflecting surfaces S₅ and S₄,respectively, orthogonal to these longitudinal lines are parallel to oneanother and accordingly orthogonal to the optical axis.

In the 25° embodiment of the prism of the invention shown in FIGS. 6through 10, it is possible to select the index of refraction of thematerial of the prism 36 with respect to the angle of incidence of therays on the second reflecting surface S₅ such that reflection of therays takes place entirely within the prism, due to total internalreflection, and so that no reflective coating is required on surface S₅,simplifying the manufacture of the prism.

The preferred material of the prism is injection molded plastic. Asuitable material known as NAS is a copolymer of 70% polystyrene and 30%acrylic. A particularly suitable choice is NAS30 material, sold byPolysar, Inc., having an index of refraction of 1.564 and a dispersionof 35.0. (Throughout this specification and the appended claims, allvalues for indices of refraction refer to the index of refractionmeasured with respect to the "D-line" in the sodium spectrum, as isconventional.)

A reflective coating 73, e.g., of aluminum, is required on surface S₄.Preferably the end surfaces S₃ and S₆ are provided with ananti-reflection coating to insure maximum transmission of the lightbeing gathered. The second reflective surface S₅ should be leftoptically clear for total internal reflection.

In some embodiments of the invention it may be desired to provide anopaque baffle 74 within the recess 90 to prevent stray light fromentering the optical path through surface S₅. The lower extremity ofbaffle 74 must be spaced from the reflecting surface S₅.

As shown in FIG. 10 and also in FIG. 3, a concave lens surface S₂ isformed in the glass window element 34 to which the front surface S₃ ofthe prism 36 is juxtaposed. This concave lens surface S₂ is centeredabout the axis of the field of view 100. The function of this concavelens surface S₂ is to collect light from a broad field of view.

In order that light gathered by lens surface S₂ can be efficientlytransmitted by the prism, it is important that a region 108 (FIG. 9) onsurface S₃ remain optically clear. In the particular implementation ofthe endoscope of the invention specified by Table I below (in which eachof the elements of the probe 10 are of 3.5 mm outside diameter), thisregion 108 is approximately 1.5 mm in diameter. Similarly, the rearsurface S₆ (FIG. 6) of the prism should have a clear aperture 110 atleast 1.525 mm in diameter. A central section 112 (FIG. 7) of firstreflecting surface S₄, approximately 1.27 by 1.00 mm, similarly must beclear prior to application of reflective coating 73, and the secondreflecting surface S₅ (FIG. 9) should include a rectangular clearaperture 114 typically measuring 1.27 by 0.90 mm.

Preferably the prism 36 is manufactured by injection molding. A suitablemold 120 is shown in FIG. 11. The mold 120 includes a mold cavity 112generally conforming to the cylindrical outline of the prism, having oneend orthogonal to the cylindrical axis and one oblique end, conformingto the surfaces S₆ and S₃ of the prism, respectively. The mold 120includes two opposed slide members 124 and 126 to be controllablyinserted into and withdrawn from the mold cavity 112. The slide members124 and 126 have distal tips corresponding in shape to the desiredrecesses 90 and 92 in the prism. Manufacture of the prism simplyinvolves the steps of inserting the slide members 124 and 126 into themold cavity, injecting the appropriate Polysar NAS30 acrylic material,allowing it to cool and harden, withdrawing the slide members 124 and126 from the mold cavity 112 to the positions shown in FIG. 11, andwithdrawing the hardened prism precursor 128 from the mold cavity. Thefirst reflecting surface S₄ is then coated with suitable reflectivematerial, and the remaining critical surfaces are coated with a suitableanti-reflection coating.

The optical parameters of the other elements of a particularimplementation of the endoscope will now be summarized, after whichthere is provided Table I detailing each of the critical opticalparameters of this implementation of the invention.

In the following, optical components having flat or spherical surfacesare specified by definition of the radii of their ends, the index ofrefraction and the dispersion of their materials, and by their thicknessalong the optical axis. Aspheric surfaces are defined in thisspecification and the appended claims by the values needed to completethe following equation: ##EQU1## wherein: A, B, C, and D are constants;

k is the conic constant of the surface;

c is the basic curvature of the surface, such that c=1/R in the casewhere k=A=B=C=D=0, and the equation defines a spherical surface ofradius R; and

z is the sagitta, that is, the distance between a plane tangent to theaspheric surface at the optical axis and all points P (h,z) on thesurface a radial distance h measured orthogonal to the optical axis.

FIG. 12 explains the values of the variables z and h appearing in thisequation. Points P (h,z) define the aspheric surface, appearing in twodimensions as a parabola. All points P (h,z) lie on a circle of radius h(or "semi-diameter", in optical parlance) on the aspheric surface, wherez is the sagitta, that is, is the length of a normal from the planetangent to the spherical surface at the optical axis to the circle.

As indicated by the equation above, the curvature of an aspheric surfaceis defined by four constants A, B, C and D, the conic constant k, and c,the basic curvature of the surface. Specifically, curvature c=1/R, whereR is the radius of the spherical surface defined by the equation givenabove in the special case where the conic constant k and constants A, B,C and D are all set equal to zero.

This method of defining an aspheric surface is an industry standard andfamiliar to those skilled in the art.

Accordingly, the aspheric surfaces of the exemplary implementation ofthe optical system of the endoscope of the invention are adequatelydescribed in Table I by listing values for A, B, C, D, c, and k. Thecurvature c is specified by giving the inverse value of the base radiusR. Similarly, in the claims appended to this specification, asphericsurfaces are defined by provision of these six values, and reference isto be made to the equation above for their definition.

As is conventional in the optical art, the spherical elements of anexemplary implementation of the endoscope of the invention are specifiedin Table I by the radii of their surfaces (a negative sign indicatingthe center of the surface is disposed more closely to the distal tip ofthe probe than is the surface, as is conventional), the thickness of theelement, and the index of refraction and dispersion of the material. Thesurfaces S₁ -S₇₁ appearing in Table I are specifically identified inFIGS. 3-10. Table I further includes specification of the suitablematerials for each of the elements.

Thus, for example, the window 34 at the tip of the probe is shown byTable I to be formed of type LAF2 optical glass having index ofrefraction 1.744 and dispersion 44.72. Its outer surface S₁ is planar(i.e., of infinite radius) and its inner surface S₂ concave and of1.1765 mm radius. The central thickness of window 34 measured along thecenter of the field of view is 0.762 mm. Surface S₂ is centered on axis100, the center of the field of view of the system. Axis 100 is at 25°to the optical axis of the probe in this implementation of theinvention. The outer planar surface S₁ of the glass window 34 isorthogonal to the axis 100.

The next element in the objective section 24 of the probe 10 is theprism, as discussed above in detail. As there indicated, the prism ismolded of Polysar NAS30 plastic, having a index of refraction of 1.564and dispersion of 35.0. The front surface S₃ at which the prism 36 isjuxtaposed to the window 34 is inclined at an angle of 25° to theoptical axis; its first reflective surface S₄, having a reflectivecoating 73 thereon, is inclined at angle B of 21.5° to the optical axis.The inclination of surface S₄ is specified in Table I by the angle of43.5° between S₄ and the entry surface S₃ of the prism 36. Secondreflecting surface S₅ of the prism 36 is inclined at 34° to the opticalaxis; this relation is specified in Table I by the 56° angle, angle C,between S₅ and the proximal planar end S₆ of the prism 36.

Lenses 38 and 40 have identical surface curvatures, but are reversedwith respect to one another. Thus the surface S₇ of lens 38 disposedtoward the prism, and surface S₁₀ of lens 40 disposed toward the thirdlens 42 of the objective group have the same 3.302 mm convex radius,while their facing surfaces S₈ and S₉ are convex aspheric, havingspecifications which will be found in the Table. Lenses 38 and 40 aremolded of polymethylmethacrylate ("PMMA") plastic, for example, Rohm andHaas Company V920 acrylic plastic having an index of refraction of 1.492and dispersion of 57.4. The central thickness of lenses 38 and 40 is2.286 mm. Other grades of acrylic molding resins may be satisfactory.

The third lens 42 of the objective group is formed of Polysar NAS30plastic, again having an index of refraction of 1.564 and dispersion of35.0. Its concave surface S₁₁ facing toward the prism is of 7.126 mmradius and its surface S₁₂ disposed toward the transfer module is alsoconcave, with a radius of 4.942 mm.

As shown in FIG. 3, each of lens 38, 40 and 42 are formed to compriseintegral spacers, so that their surfaces are spaced by air gaps thelengths of which are specified in Table I.

The next optical element in the endoscope of the invention is theentrance rod 44 of the transfer module assembly 26. Rod 44 is 12.70 mmlong, plano-ended, and made of BASF2 glass, having an index ofrefraction of 1.6644 and a dispersion of 35.83. Entrance rod 44 isspaced from the third lens 42 of the objective group by a spacer 82. Theinside surface of spacer 82 provides the field stop for the system,appearing as S₁₃ in Table I. The inside diameter of the field stop is2.05 mm. The axial spacing between the proximal surface S₁₂ of lens 42and the distal surface S₁₄ of the first glass rod 44 of the transfermodule assembly 26 is given in Table I and totals 2.684 mm.

As noted, according to an important aspect of the invention, each of thefive glass rods 45, 46, 47, 48 and 49 of the relay modules 28, 30 and 32of transfer module assembly 26 are identical. Each of the five rods45-49 has a central length of 28.575 mm, has planar end surf aces ofinfinite radius and is also formed of BASF2 optical glass. The fact thatthese rods 45-49 are all identical and that all of the rods 44-50 of thetransfer module assembly have planar end surfaces contributes materiallyto making the endoscope of the invention sufficiently inexpensive thatit can be cost effective for single patient, disposable use.

As discussed above, FIG. 4 shows the transfer module assembly 26 whichcomprises seven glass rods 44, 45, 46, 47, 48, 49 and 50, and twelvelenses 52 and 53, arranged as six doublets. The transfer module assembly26 thus comprises three substantially similar relay modules, 28, 30 and32, each including an entry rod, a first doublet, an intermediate rod, asecond doublet, and an exit rod. The exit rod of one relay module andthe entry rod of the next may be configured as a single continuousmember, as shown, to reduce the number of parts and of optical surfaces.The transfer module assembly as shown may also be considered to comprisesix relay subgroups 33, each consisting of a doublet and a plano-endedglass rod, together with entry rod 44.

As discussed above, the elements 52 and 53 of the first doublet of eachrelay module are optically identical to the elements 52 and 53respectively of the second doublet, but are physically reversed. Thedistal entry surface S₁₆ of the first element 52 of the first doublet isthus optically identical to the proximal exit surface S₂₅ of the secondelement 52 of the second doublet. As specified in Table I, thesesurfaces are convex with radius 9.233 mm. The thickness of element 52along the optical axis is 1.778 mm and the radius of the opposingsurface, e.g., surface S₁₇ of the first element 52, is 4.335 mm.Elements 52 are molded from Polysar, Inc. NAS30 plastic which as abovehas an index of refraction of 1.564 and a dispersion of 35.0.

The second element 53 of each doublet is similarly identical. Theelements 53 each contact the corresponding elements 52, e.g., at surfaceS₁₈ for the first element 53, which accordingly is convex with a radiusof 4.335 mm. The other surfaces of each of these elements, e.g. S₁₉ forthe first element 53, are aspheric having characteristics defined byTable I. Elements 53 have an axial thickness of 2.286 mm and are formedof polymethylmethacrylate (PMMA) plastic, e.g., Rohm and Haas CompanyV920 acrylic plastic, having as mentioned above an index of refractionof 1.492 and dispersion of 57.4.

The last rod element 50 in the transfer module assembly 26 is alsoformed of BASF2 glass, is plano-ended and is 6.35 mm long.

The transfer module assembly is terminated by a window 56 havingsurfaces S₅₂ and S₅₃. As shown in Table I these surfaces are bothoptically flat, specified as of infinite radius. The window 56 is 1.000mm thick and is formed of type BK7 optical glass, having index ofrefraction 1.516 and dispersion 64.17.

The focusing ocular meets the transfer module at a generally similarwindow 58 having surfaces S₅₄ and S₅₅. The radii of these two planarsurfaces are infinite. Window 58 is also 1 mm thick and of type BK7glass.

As shown in Table I, the entry surface S₅₇ of the distal element 59 ofthe movable focusing doublet comprising lenses 59 and 60 is of infiniteradius and its exit surface S₅₈ is concave of 6.573 mm radius. Thecentral thickness of element 59 is 2.032 mm. Element 59 is formed oftype SK5 optical glass having index of refraction 1.589 and dispersion61.27.

The second lens 60 of the focusing doublet is cemented to the first lens59. Accordingly a single entry in Table I is provided for surface S₅₈,specifying the mating surfaces of elements 59 and 60. The second element60 of the focusing doublet is formed of type F8 optical glass of indexof refraction 1.595 and dispersion 39.18, is 2.681 mm thick, and has anexit surface S₅₉ of 14.126 mm radius. In the preferred embodiment thefocusing doublet comprising elements 59 and 60 is provided with axialmotion of at least about 2.54 mm to enable focusing of the endoscopefrom the front surface of the window 34 to infinity. An aperture stop 61is provided between the doublet consisting of lenses 59 and 60 and thedoublet consisting of lenses 62 and 64. The axial location of aperturestop 61 is specified by S₆₀ in Table I.

The first element 62 of the second doublet of the ocular as shown inTable I has an convex entry surface S₆₁ of 9.824 mm radius and exitsurface S₆₂ which is convex with a radius of 3.81 mm. This lens has acentral thickness of 4.572 mm and is formed of type SK16 optical glasshaving a index of refraction of 1.620 and dispersion of 60.33.

As elements 62 and 64 of the second doublet are cemented to one another,a single entry for surface S₆₂ defines their mating surfaces. Exitsurface S₆₃ of lens 64 is of infinite radius, and its thickness is 2.032mm. The material of lens 64 is type LAF2 optical glass having index ofrefraction of 1.744 and dispersion of 44.72.

The second doublet is spaced by an air gap given in Table I from a thirdairspaced doublet consisting of a first lens 66 and a second lens 68.Entry surface S₆₄ of the first lens 66 is convex of radius 8.604 mm andexit surface S₆₅ is convex of radius 8.604 mm. The central thickness ofthis lens 66 is 3.81 mm. Lens 66 is formed of type SK5 optical glasshaving an index of refraction of 1.589 and dispersion of 61.27.

The second lens 68 of the third airspaced doublet has a entry surfaceS₆₆, concave with a radius of 2.908 mm. Its exit surface S₆₇ is ofinfinite radius and its central thickness is 2.032 mm. Element 67 isformed of type SF11 optical glass having an index of refraction 1.784and dispersion equal to 25.76.

The last three elements in the system are filters and windows providedin the preferred CCD video camera. As discussed above, element 70 is aspatial filter provided in certain preferred Sony video cameras, element71 is a spectral filter removing infrared radiation from the imagedlight, and element 72 is a protective window. Table I provides thecritical specifications of elements 70-72. Surface S₇₁ is the activesurface of the CCD imaging element of the video camera 22. As notedabove, the presence of elements 70-72 is not required.

Table I following summarizes the optical specifications just given, andadditionally provides the specifications of the aspheric surfaces moldedon the various plastic elements. Table I also provides all relevantairspaces and other information not specifically given above. Table Ialso reflects the fact that a drop of distilled water may usefully beplaced between the windows 56 and 58 of the probe and ocular,respectively, to exclude air and prevent fogging due to condensation.Table I thus provides a complete optical prescription for a disposableendoscope; from this information, one of skill in the art would have nodifficulty in constructing an endoscope according to the presentinvention.

                                      TABLE I    __________________________________________________________________________      Radius (mm) or      Aspheric Terms               Thickness    Refractive                                  Dispersion    Sn      or (Tilt Angle)               (mm) Medium  Index (Nd)                                  (Vd) Element                                              Assembly    __________________________________________________________________________     1      INFINITY   0.762000                    LAF2    1.74400                                  44.72                                       window/ele 1                                              Objective Group     2        1.17650                 0.270000                    AIR                (34)   (24)     3      INFINITY   1.651000                    NAS30   1.56400                                  35.00                                       prism  |     4      INFINITY (-43.50)               -1.524000                    REFL (NAS30)       (36)   |     5      INFINITY (+56.00)                 1.778000                    REFL (NAS30)       |                                              |     6      INFINITY   0.127000                    AIR                |                                              |     7        3.30200                 2.286000                    PMMA    1.49200                                  57.40                                       lens (38)                                              |     8      c = -0.249431                 0.356564                    AIR                |                                              |      k = -1.026659                    |                                              |      A = 0.491000E-02                 |                                              |      B = 0.133746E-02                 |                                              |      C = D = 0.0                      |                                              |     9      c = 0.249431                 2.286000                    PMMA    1.49200                                  57.40                                       lens (40)                                              |      k = -1.026659                    |                                              |      A = -0.491000E-02                |                                              |      B = -0.133746E-02                |                                              |      C = D = 0.0                      |                                              |    10      -3.30200   0.241087                    AIR                |                                              |    11      -7.12576   1.651000                    NAS30   1.56400                                  35.00                                       lens (42)                                              |    12        4.94207                 1.674264                    AIR                |                                              |    13      INFINITY   1.016000                    AIR                int. image                                              |    14      INFINITY 12.700000                    BASF2   1.66446                                  35.83                                       rod (44)                                              Transfer Module    15      INFINITY   0.254000                    AIR                |                                              (26)    16        9.23300                 1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    17        4.33469                 0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    18        4.33469                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |    19      c = -0.121238                 0.254000                    AIR                |                                              |      k = -1.317139                    |                                              |      A = -0.269762E-04                |                                              |      B = 0.681709E-04                 |                                              |      C = D = 0.0                      |                                              |    20      INFINITY 28.575000                    BASF2   1.66446                                  35.83                                       rod (45)                                              |    21      INFINITY   0.254000                    AIR                |                                              |    22      c = 0.121238                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |      k = -1.317139                    |                                              |      A = 0.269762E-04                 |                                              |      B = -0.681709E-04                |                                              |      C = D = 0.0                      |                                              |    23      -4.33469   0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    24      -4.33469   1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    25      -9.23300   0.254000                    AIR                |                                              |    26      INFINITY 28.575000                    BASF2   1.66446                                  35.83                                       rod (46)                                              |    27      INFINITY   0.254000                    AIR                |                                              |    28        9.23300                 1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    29        4.33469                 0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    30        4.33469                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |    31      c = -0.121238                 0.254000                    ATR                |                                              |      k = -1.317139                    |                                              |      A = -0.269762E-04                |                                              |      B = 0.681709E-04                 |                                              |      C = D = 0.0                      |                                              |    32      INFINITY 28.575000                    BASF2   1.66446                                  35.83                                       rod (47)                                              |    33      INFINITY   0.254000                    AIR                |                                              |    34      c = 0.121238                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |      k = -1.317139                    |                                              |      A = 0.269762E-04                 |                                              |      B = -0.681708E-4                 |                                              |      C = D = 0.0                      |                                              |    35      -4.33469   0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    36      -4.33469   1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    37      -9.23300   0.254000                    AIR                |                                              |    38      INFINITY 28.575000                    BASF2   1.66446                                  35.83                                       rod (48)                                              |    39      INFINITY   0.254000                    AIR                |                                              |    40        9.23300                 1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    41        4.33469                 0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    42        4.33469                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |    43      c = -0.121238                 0.254000                    AIR                |                                              |      k = -1.317139                    |                                              |      A = -0.269762E-04                |                                              |      B = 0.681709E-04                 |                                              |      C = D = 0.0                      |                                              |    44      INFINITY 28.575000                    BASF2   1.66446                                  35.83                                       rod (49)                                              |    45      INFINITY   0.254000                    AIR                |                                              |    46      c = 0.121238                 2.286000                    PMMA    1.49200                                  57.40                                       lens (53)                                              |      k = -1.317139                    |                                              |      A = 0.269762E-04                 |                                              |      B = -0.681709E-04                |                                              |      C = D = 0.0                      |                                              |    47      -4.33469   0.000000                    CEMENT/AIR                            1.56000                                  44.00                                       |                                              |    48      -4.33469   1.778000                    NAS30   1.56400                                  35.00                                       lens (52)                                              |    49      -9.23300   0.254000                    AIR                |                                              |    50      INFINITY   6.350000                    BASF2   1.66446                                  35.83                                       rod (50)                                              |    51      INFINITY   0.000000                    AIR                |                                              |    52      INFINITY   1.000000                    BK7     1.51680                                  64.17                                       window (56)                                              |    53      INFINITY   0.254000                    AIR/WATER          |                                              |    54      INFINITY   1.000000                    BK7     1.51680                                  64.17                                       window (58)                                              Ocular (20)    55      INFINITY   3.253251                    AIR                |                                              |    56      INFINITY   2.540000                    AIR                int. image                                              |    57      INFINITY   2.032000                    SK5     1.58913                                  61.27                                       lens (59)                                              |    58        6.57332                 2.680977                    F8      1.59551                                  39.18                                       lens (60)                                              |    59      -14.12584               22.223063                    AIR                |                                              |    60      INFINITY   0.000000                    AIR                (aperture stop)                                              |    61        9.82357                 4.572000                    SK16    1.62041                                  60.33                                       lens (62)                                              |    62      -3.81000   2.032000                    LAF2    1.74400                                  44.72                                       lens (64)                                              |    63      INFINITY   3.623418                    AIR                |                                              |    64        8.60409                 3.810000                    SK5     1.58913                                  61.27                                       lens (66)                                              |    65      -8.60409   3.621807                    AIR                |                                              |    66      -2.90783   2.032000                    SF11    1.78472                                  25.76                                       lens (68)                                              |    67      INFINITY 12.700000                    AIR                |                                              |    68      INFINITY   2.000000                    FUSED SILICA       spatial fil (70)                                              Camera (22)    69      INFINITY   2.350000                    BK7     1.51680                                  64.17                                       IR filter                                              |    70      INFINITY   1.500000                    FUSED SILICA       window |    71      INFINITY   0.000000                    AIR                (image plane)                                              |    __________________________________________________________________________

The endoscope defined by Table I above has a field of view approximately68° wide centered on an axis 25° from the optical axis of the probe, anda focal length of 1.3 mm in the anticipated saline environment.

FIG. 13 is a complete ray-tracing diagram of the endoscope of theinvention showing the respective paths through the endoscope of lightrays from various portions of its field of view FOV. Light collectedfrom the field of view FOV is formed into an image by objective 24, andthe image is reformed at four intermediate image locations IL. The firstintermediate image location IL is between the objective 24 and thetransfer module assembly 26, as shown; the second and third intermediateimage locations are between the relay modules 28 and 30, and 30 and 32,respectively; and the fourth intermediate image location is between thetransfer module assembly and the ocular 20. As noted, by forming thesecond and third intermediate images within continuous glass rods 46 and48 of the transfer module assembly, rather than at the surfaces ofoptical elements, the effect of any surface imperfections on theultimate image is eliminated. FIG. 13 also shows the aperture stop 61;images of the aperture stop appear at locations AS within the prism 34and at intermediate points within each relay module.

Thus, it will be appreciated that an important aspect of the method ofthe invention of forming a visible image of an interior of a body cavityor the like is the step of forming intermediate images between theobjective and the transfer module assembly, and between each of therelay modules. Further, as discussed above, the image formed by theobjective and thus transmitted to the ocular by the transfer moduleassembly includes certain predetermined aberration (particularly axialand lateral chromatic aberration, and field curvature) corrected by theocular according to the method of the invention.

Numerous conventional techniques may be of use in practicing theinvention. For example, it is well known to coat optical surfaces atwhich an air gap exists with an antireflection coating, to minimizelight loss. Known multi-layer dielectric coatings are preferred for thispurpose; a magnesium fluoride film of approximately 137.5 nm thickness,that is, equal to one-quarter the wavelength of light in the center ofthe band to be collected, is also satisfactory. The circumferentialsurfaces of the various elements may be blackened to absorb stray light.The outer peripheral surfaces of each of the elements are cylindrical,specifically 3.5 mm diameter in the embodiment described herein indetail, so that the probe may be assembled simply by inserting theelements in sequence into the bore of a tube. These and other aspects ofpractice of the invention are within the skill of the art.

The design of the endoscope according to the invention having thus beenspecified in detail, its advantages and improvements over the prior artcan now effectively be summarized.

According to an important aspect of the invention, most of the surfacesof the glass elements of the disposable probe 10 are planar. The soleexception is the spherical surface S₂ formed in the distal windowelement 34. The remaining elements of the disposable probe 10 havingcurved optical surfaces are inexpensively molded of plastic. While theoptical elements of the ocular 20 are of glass, the ocular is notdisposable so that its cost does not contribute significantly to theper-use cost of the endoscope according to the invention.

The preferred design specified above includes a number of molded plasticlenses having aspheric surfaces which are relatively easy to form usingpresently available technology. As noted, as glass molding technologymatures, it may become desirable to mold some or all of the lenses ofthe probe of glass. It will be recognized that some of the asphericsurfaces could also be eliminated through use of appropriatenonhomogeneous optical materials, that is, materials exhibitinggradients in their index of refraction. Elements employing thesematerials are intended to be included within the claims of thisapplication where not specifically excluded.

It will also be appreciated by those of skill in the art that the use ofan integrally molded prism according to the invention providessubstantial economy as compared to the complex prism fabricationtechniques employed in the prior art. According to the invention,endoscopes comprising prisms molded of plastic can be manufactured atsufficiently low cost to be cost-efficient for single-patient,disposable use; in the future it may become preferable to mold the prismof glass.

In the following claims, it is to be understood that each of the opticalelements (apart from the prism) includes first and second opticalsurfaces, that is, surfaces intersecting the optical axis. The opticalsurfaces of the various elements may be unambiguously identified byreference to their respective positions within the probe, for economy oflanguage. Where the claims refer to the specific optical parameters ofvarious elements of the probe, the elements are identified and specifiedas in Table I above. As used in the attached claims, the terms "opticalelement" and "element" are to be understood to refer to members havingoptical power, that is, having at least one curved surface. The term"doublet" is to be understood to refer to a combination of two suchoptical elements. Where aspheric surfaces of the various elements of theprobe of the invention are specified numerically, the signs of thevalues for the aspheric constants A and B are given in relation to thesign of the curvature c of the corresponding element; that is, the signsof constants A, B and c vary with respect to the orientation of thecorresponding surface, as shown by Table I.

It will be understood that reference herein to the fact that the probeof the endoscope of the invention is cost effective for single-patientdisposable use should not be construed to limit the invention defined bythe following claims, nor to preclude non-disposable, multiple-patientuse of the invention.

Inasmuch as the present invention is subject to many variations,modifications and changes in detail, it is intended that all subjectmatter discussed above or shown in the accompanying drawings beinterpreted as illustrative only and not be taken in a limiting sense.

What is claimed is:
 1. A unitary molded prism for an objective group ofan elongated endoscope probe for imaging an interior of a cavity,comprising:an elongated generally cylindrical member having a firstdistal entry end inclined at a first angle to an optical axis of adisposable endoscope probe, and a plano second proximal exit endorthogonal to the optical axis of the probe, and having first and secondplanar reflective surfaces formed by inward terminations of first andsecond recesses in an outer surface of said prism, such that light rayswithin a field of view of said prism entering said prism at said distalentry end reflect internally within said prism from said first andsecond reflecting surfaces and exit said prism through said plano secondexit end; and wherein said second reflecting surface is inclined withrespect to the optical axis of the probe at an angle different than saidfirst angle between the first distal entry end of the probe and theoptical axis.
 2. The unitary molded prism of claim 1, wherein therefractive index of the material of said prism and the relativeorientation of said entry end and said first and second reflectivesurfaces are such that reflection of said rays from one of saidreflective surfaces takes place by total internal reflection at aninterface between the material of said prism and air, said interfacebeing defined by said reflecting surface.
 3. The unitary molded prism ofclaim 1, wherein the inward termination of one of said recesses iscoated with a reflective material.
 4. The unitary molded plastic prismof claim 1, further comprising an optically opaque baffle disposed inone of said recesses.
 5. The unitary molded plastic prism of claim 1,wherein said first and second planar reflective surfaces are disposedsuch that imaginary longitudinal lines in the planes of and bisectingsaid first and second planar reflective surfaces intersect the opticalaxis of said probe, and transverse lines on said first and second planarsurfaces orthogonal to the longitudinal lines are parallel to oneanother.
 6. The unitary molded plastic prism of claim 5, wherein a planeincluding said first reflective surface intersects said optical axis atan angle of approximately 21.5° and a plane including said secondreflective surface intersects said optical axis at an angle ofapproximately 34°.
 7. The unitary molded plastic prism of claim 1,wherein said prism is molded of type NAS30 copolymer having refractiveindex 1.564 and dispersion 35.0.
 8. The unitary molded prism of claim 1,wherein the angle between the first reflecting surface and the plane ofthe first distal entry end of the probe is other than half said firstangle between the first distal entry end of the probe and the opticalaxis.
 9. A method of manufacture of a unitary optical prism of moldableoptical material, said prism consisting of an axially elongated memberhaving one end at an angle to an axis of elongation of said member andone planar end orthogonal to the axis of said member, and having tworecesses extending into a body of said member from opposite sidesthereof, said recesses each being terminated by planar surfaces, saidmethod comprising the steps of:providing a mold means, said mold meansdefining a mold cavity conforming to an outline of said axiallyelongated member, said mold means comprising first and second slidemembers, said slide members being controllably inserted into andwithdrawn from said mold cavity, said slide members having distalsurfaces conforming to desired surface contours of said recesses;inserting said slide members in said mold cavity; injecting a quantityof a suitable moldable optical material into said mold cavity; allowingsaid material to solidify in conformance to contours of said mold cavityand the distal surfaces of said slide members; withdrawing said slidemembers from said mold cavity; and withdrawing said solidified materialfrom said mold cavity.
 10. The method of claim 9, comprising the furtherstep of assembling an opaque baffle in one of the recesses in saidsolidified material.
 11. The method of claim 9, comprising the furtherstep of providing a reflective coating on a planar surface terminatingone of said recesses.
 12. The method of claim 9, wherein said moldableoptical material is type NAS30 acrylic plastic material having an indexof refraction of substantially 1.564, and dispersion of 35.0.